Production of adrenal steroids in intact and castrated dogs is stimulated acutely by ACTH. While the increase in plasma cortisol, 17-hydroxypregnenolone and 17-hydroxyprogesterone is not affected by castration, the increment of dehydroepiandrosterone is totally abolished. On the other hand, administration of 17-hydroxypregnenolone in adrenalectomized dogs caused an increase in plasma C-19 steroids such as dehydroepiandrosterone, androstenedione and testosterone indicating that this C-21 progestin in plasma is rapidly converted. The site of this conversion is likely the testis. Furthermore, acute hCG administration in adrenalectomized dogs resulted in a marked increase in the levels of plasma 17-hydroxypregnenolone and dehydroepiandrosterone. However, our data show an ACTH-induced rise in 5-androstene-3 beta. 17 beta-diol in intact and castrated dogs, thus suggesting that this steroid is a good parameter to assess in the stimulation of adrenal steroidogenesis by ACTH.